In traditional safety detection technologies for nuclear materials, it is a common technology to use 3He proportional counters and polyethylene moderators for fast-neutron detection. However, this technology at least has the following two drawbacks:
1. The supply of 3He gas is insufficient. Since 3He is an important nuclide for detecting neutron, the insufficient supply problem of 3He which has been occurring commonly throughout the world has already imposed a serious challenge to application of nuclear material security detection technologies so that manufacturing costs of security apparatuses rise abruptly.
2. In this technology, the moderated volume and the measured volume of neutrons are independent on each other, i.e., the moderated volume is constituted by polyethylene whereas the measured volume is constituted by 3He proportional counter. The moderated volume is in a competitive relation to the measured volume in space, and a final detection efficiency depends on a product of a fast-neutron moderating efficiency and a thermal neutron absorbing efficiency to which the moderated volume and the measured volume correspond respectively, whereby the moderated volume cannot be made too large, nor the measured volume can be made too large, which limits the maximum fast-neutron detection efficiency achieved by this technology.